Typical transimpedance amplifiers convert current input signals into a voltage signal through a linear process. The output is basically the input signal only amplified and changed from a current to a voltage. For very fast signals, this transimpedance amplifier needs to have a large bandwidth to follow the input signal. With traditional designs, it is very difficult to get large bandwidth without careful layout and design of the circuit, which greatly increases the time and cost of manufacture.
Conventional transimpedance amplifiers use AC-coupled circuits. These AC-coupled circuits can only be used for continuous data streams due to the time associated with charging the coupling capacitors. In most applications where the amplifier must be burst mode ready, the data stream must either be preceded by an identifying string of binary signals, to give the amplifier time to conform, and/or the amplifier must include sophisticated DC bias restore circuitry. Either of these solutions increase the cost and complexity of operation.
Further, the sensitivity of prior art transimpedance amplifiers was generally adversely effected by input loading. The sensitivity of a transimpedance amplifier can be defined as the minimum input which will produce no errors in the output. Generally, the sensitivity is a strong function of parasitic capacitance and inductance at the input stage or stages. Thus, in the prior art AC-coupled transimpedance amplifiers, virtually anything done at the front end, such as edge triggering, would tend to reduce or adversely impact sensitivity.